A CCD (Charge-Coupled Device) image sensor is an image sensor that arranges two-dimensionally photoelectric conversion devices (e.g., photodiodes) corresponding to pixels, and reads out signals of respective pixels that are electric charges provided by the photoelectric conversion devices using a vertical transfer CCD and/or a horizontal transfer CCD.
On the other hand, a CMOS (complementary metal-oxide-semiconductor) image sensor is similar to the CCD image sensor in that the photoelectric conversion devices corresponding to pixels are two-dimensionally arranged, but does not readout signals using the vertical and horizontal transfer CCDs, and instead reads out the signals stored per pixel from the pixels selected using selection lines configured of aluminum, copper wire, etc. like a memory device.
As described above, the CCD image sensor and the CMOS image sensor are different in many points such as a readout method, but are common to have photodiodes.
A maximum value of a signal electric charge quantity accumulated on the photoelectric conversion devices is referred to as a saturated signal electric charge quantity (Qs). An image sensor having a high saturated signal electric charge quantity has improved dynamic range and signal to noise (SN) ratio. Accordingly, an increase of the saturated signal electric charge quantity is a desirable property improvement of the image sensor. As a method of increasing the saturated signal electric charge quantity, it is conceivable that an area of the photodiode is increased, or that a PN junction capacity of the photodiode is increased.
Patent Literature 1 suggests an image sensing device that can provide high sensitivity by increasing a saturated signal electric charge quantity without increasing an area of a photoelectric conversion device and an impurity concentration.